Present day brush commutated electric motors include an armature having a plurality of coils wound in slots formed in the lamination stack of the armature. With traditional motor designs, the lamination stack of the armature forms a plurality of circumferentially arranged slots extending between adjacent pairs of lamination posts. Typically, two coils per slot are used when winding the armature coils on the lamination stack. Among the two coils of the same slot, the one which commutates first is referred to as the first coil and the one which commutates second as the second coil. The second coil has inherently poorer magnetic commutation than the first coil because the second coil passes beyond the magnetic neutral zone within the stator before it finishes commutation. This is illustrated in simplified fashion in FIG. 1, wherein the commutation region of the first coil is designated by Z1 and the commutation region of the second coil is designated by Z2. A rotor “R” is shown positioned within a stator “S” having field coils “F”. This is further illustrated in FIGS. 1a-1f. FIGS. 1a and 1b illustrate the position of the magnetic axis of the first and second coils, respectively, relative to the commutation regions Z1 and Z2 of each coil. FIGS. 1c and 1d illustrate the position of the magnetic axis of each of the first and second coils, relative to the field pole and brush, at the start of commutation of each coil. The magnetic axis of the first coil, in this example, is retarded about 22.5 degrees from the axis of the field pole and the brush (FIG. 1c), while for the second coil, its magnetic axis is only retarded about 7.5 degrees relative to the field pole and brush (FIG. 1d). FIG. 1e shows the angular position of the magnetic axis of the first coil, relative to the field pole, when the first coil ends commutation. FIG. 1f shows the angular position of the magnetic axis of the second coil, relative to the field pole and brush, when the second coil ends commutation. The angular position of the second coil, when it ends commutation, is clearly past the angular position, relative to the field pole, at which the first coil ends its commutation. The two regions Z1 and Z2 are not commonly angularly aligned (i.e., coincident) relative to the field pole and brush. As a result, the second coil commutation can generate significant brush arcing, and becomes the dominant source of the total brush arcing of the motor. This can also cause electro-magnetic interference (EMI) to be generated which exceeds acceptable levels set by various government regulatory agencies. This brush arcing can also lead to accelerated brush wear.
Accordingly, it is a principal object of the present invention to provide an armature for a brush commutated electric motor having a plurality of coils wound thereon in a unique sequence which serves to significantly reduce brush arcing and improve the commutation efficiency of the motor.
It is a further object of the present invention to provide an armature for a brush commutated electric motor which incorporates a unique winding pattern for the coils wound on the armature in a manner which does not otherwise require modification of any component of the armature or the need for additional components.
It is still a further object of the present invention to provide a winding pattern for the armature coils of an armature which allows EMI components usually required to sufficiently attenuate the EMI generated by brush arcing to be eliminated, thus allowing the motor to be constructed less expensively and with fewer components.